1. Field of the Invention
The invention generally relates to an optical system and an optical apparatus and, in particular, to an illumination system and a projection apparatus.
2. Description of Related Art
A conventional projection apparatus with high brightness generally adopts ultra high pressure (UHP) lamp as light source. However, in the trend of green energy, many countries are gradually inhibiting the use of lamp with mercury. As a result, finding a substitutive environmentally friendly light source for the projection apparatus becomes a main issue in the field of the projection apparatus.
Light-emitting diodes (LEDs) have been broadly used in various fields of light sources. LEDs have a long lifespan and high color saturation and are environmentally friendly due to power saving and no mercury contained. However, the brightness of current LEDs has not achieved the level of brightness of UHP lamps, so that the projection apparatuses with LEDs can still not completely replace the projection apparatuses with UHP lamps.
A conventional technique uses a light with short wavelength to excite a phosphor to achieve higher brightness. For example, U.S. patent application publication No. 20100328632 discloses a light source system including a plurality of blue light sources, reflective mirrors, a color wheel, light guide element. The color wheel includes a green phosphor layer and a red phosphor layer. PRC patent publication No. 101498415 discloses an illumination light source including a light source, a beam splitting filter, an excited material layer, a first reflective surface, a second reflective surface, and a rotation shaft.